High-voltage fuse

ABSTRACT

A high voltage fuse with a helically wound fuse link includes an arc-extinguishing filler of quartz sand and a low thermal conductivity arc-extinguishing filler, both fillers having an interface. The low thermal conductivity filler is so densely packed as to preclude mixing of the fillers. The helically wound fuse link is supported by insulating plates parallel to the axis of the fuse casing having axially outer edges engaging grooves formed in the axially inner end surfaces of a pair of terminal plugs closing the axially outer ends of the fuse casing. The terminal plugs are provided on the outer end surfaces thereof with coaxial multifunction projections.

United States Patent (72] Inven or Frederittk J. Kozacka 3,2l3,242 lO/l965 Cameron 337/158 (X) South Hampton, NH. 3,145,282 8/1964 Gezeczkowski l 337/231 12]] Appl. No. 876,445 2,918,551 12/1959 Kozacka H 337/244 [22] Filed Nov. 13,1969 2,740,187 4/1956 Jacobs, Jr. et al t v l .l 337/159 (X) [45] Patented Aug. 10,197] P 4 E G H [73] Assignee The Chase-Shawmut Company '"Y i Newburypon Mass. Assistant Exam ner-- Dewitt M. Morgan Anorney-Erwin Salzer [54] HIGH-VOLTAGE FUSE 5 Claims, 4 Drawing Figs.

ABSTRACT: A high voltage fuse with a helically wound fuse [S2] U.S.Cl 337/159, link includes an arc extinguishing n f quartz sand and 3 337/229 337/276 low thermal conductivity arc-extinguishing filler, both fillers (51] lnt.CI ..H0lh.85/08, having an interface The low thermal conducivny fill is so 85/14 densely packed as to preclude mixing of the fillers. The heli- [50] Field of Search 337/158) cally wound fuse link is supported by insulating plates parallel 23L 33144276178193 to the axis of the fuse casing having axially outer edges engagin rooves formed in the axiall inner end surfaces of a pair [56] References cued of te rminal plugs closing the axi lly outer ends of the fuse cas- UNITED STATES PATENTS 3,291,942 l2/ 1966 Kozacka .t

ing. The terminal plugs are provided on the outer end surfaces thereof with coaxial multifunction projections.

PATENTEU AUG] 0 l9?! INVENTOR: FREDERICK J. KOZACKA ATTY.

HIGH-VOLTAGE FUSE BACKGROUND OF INVENTION In the early period of the development of current-limiting 5 fuses it appeared to be desirable to use as arc-quenching fillers mixtures of quartz sand and other pulverulent materials. In such fuses there is a tendency of separation of the two fillers as a result of which the operation of such fuses becomes unpredictable. Many modern current-limiting fuses include often two bodies of arc-quenching filler of which one is generally quartz sand and the other is a low thermal conductivity pulverulent substance, both arc-quenching fillers being separated by a barrier to preclude any mixture thereof. The quartz sand is capable of absorbing large amounts of are energy and is, therefore, responsible for a rapid decay of major fault currents to zero. The low thermal conductivity filler is generally not fulgurite forming and forms an insulating barrier interrupting the fulgurite when hot and current-conductive, and thus precludes the flow of small follow-currents after a current zero has been reached. In fuses for relatively high circuit voltages, eg 2 to k. the fusible element or fuse link must often be wound substantially helically in order to be able to accommodate in a casing of given length a fuse link whose length exceeds significantly the length of the casing. In fuses having helically wound fuse links it becomes virtually impossible to provide a barrier to separate two arc-quenching fillers in which one may wish to submerse different sections of the helically wound fuse link.

In the early period of the development of current-limiting high-voltage fuses the fuse link was generally wound helically upon a mandrel of ceramic material which was star shaped in cross section so as to support the fuse link only at discrete points, the sections of the fuse link situated between these discrete points being submersed in a pulverulent arc-quenching filler, normally quartz sand. The presence of the ceramic mandrel greatly reduced the space within a given fuse casing or fuse tube available to accommodate the heat absorbing, pulverulent arc-quenching filler. A new generation of high-voltage fuse's did not include the link supporting mandrel, and thus made it possible to accommodate in the casing of the use a relatively larger amount of quartz sand. This was achieved by winding the fuse link upon a temporary mandrel, and withdrawing or removing the samein the process of filling the fuse with the pulverulent arc-quenching filler which then assumed the function of supporting the portions of the fuse link from which'the temporary mandrel had been withdrawn. Prior art high-voltage fuses without mandrel for supporting the fuse link, or fusible element, are subject to serious limitations or drawbacks. Their manufacture calls for the relatively difficult operation of removing the temporary mandrel during the process of filling the fuse with a pulverulent arc-quenching filler or, in other words, the manufacture of such fuses calls for relatively skilled labor. Even if skilled labor is used for the manufacture of such fuses, such designs must include fuse links of relatively considerable mechanical strength, or relative thick fuse links. Relatively thin and consequently fragile fuse links require a mandrellike link support. Since it is desirable in the interest of maximizing the surface of interaction between the arc and the surrounding arc-quenching filler to minimize the thickness of fuse links, there is an urgent need for providing high-voltage fuses having a mandrellike support for a helically wound fuse link whose bulk is minimal, and thus does not significantly reduce the space for the pulverulent arcquenching filler which is available within a casing of given size. The invention offers a simple and effective solution to the problem of providing high-voltage fuses including a mandrellike fuse link support whose bulk is minimal and does not occupy any space within the fuse tube or casing at the expense of the space available for the pulverulent arc-quenching filler.

The fuses according to this invention achieve the above objects and other objects which will be apparent from what follows with simple rugged means.

The aforementioned low thermal conductivity arcquenching filler provided in certain high-voltage fuses in addition to quartz sand may serve the purpose of establishing regions of reduced heat dissipation away from the fuse link, to thereby impart to the fuse E-rating characteristics. Regions of reduced heat dissipation may be established by packing a portion of the fusible element in gypsum powder or calcium carbonate powder. The former arc-quenching medium is not very desirable on account of its relative instability. Both gypsum powder and calcium carbonate powder are subject to the limitation of generating much smaller arc voltages than silica SiO or quartz sand. Calcium carbonate generates relatively large amounts of gas when subjected to the action of electric arcs. This may be a serious limitation when achievement of the required E-rating calls for the provision of a thick layer of cal cium carbonate tending to generate excess pressures requiring fuse casings of increased mechanical strength. As the thickness of a layer of calcium carbonate is increased in a given fuse structure, the space available for the provision of quartz sand or silica S10 is reduced at the expense of the arc voltage which may be generated in the fuse.

The invention makes it possible to establish the required E- rating without resorting to the aforementioned low thermal conductivity arc-quenching fillers or, to be more specific, by using a mixture of silica Si0 in the order of 50 percent by weight and iron oxide F 0 and aluminum oxide A1 0 in the order of 20 percent by weight as low thermal conductivity arcextinguishing filler, in addition to a layer of pure quartz sand.

SUMMARY OF INVENTION Fuses embodying this invention include a helically wound fuse link which is supported by a fuse link support and of which a preponderant portion is submersed in a quartz sand arc-extinguishing filler and the remainder is submersed in a low thermal conductivity arc-extinguishing filler consisting of a mixture of silica, iron oxide and aluminum oxide. There is no partition between the quartz sand and the aforementioned low thermal conductivity arc-extinguishing filler, and there is a common interface between the quartz sand filler and the low thermal conductivity filler. The latter is rarn packed, i.e. packed so densely as to preclude mixture thereof with the quartz sand filler. I

The casings of fuses according to this invention are closed by terminal plugs having radial grooves on the axially inner surfaces thereof with equidistant lateral walls. These grooves are engaged by a plurality of plates of an electric insulating material substantially rectangular in cross section and having substantially the same thickness as the width of said grooves and extending parallel to the axis of the casing or fuse tube. A fusible element means or fuse link is wound helically around the radially outer edges of an supported by said plurality of plates of an electric insulating material and conductively interconnects said pair of terminal plugs.

BRIEF DESCRIPTION OF DRAWINGS FIG. l is a longitudinal section along I-l of FIG. 2 of a fuse embodying this invention;

FIG. 2 is a cross section along "-11 of FIG. 1 of a fuse embodying this invention;

FIG. 3 is an isometric view of the structure of FIGS. 1 and 2; and

FIG. 4 is an axial section of a detail of the structure of FIGS. 1 -3.

DESCRIPTION OF PREFERRED EMBODIMENT OF INVENTION The casing l of electric insulating material is closed on both ends thereof by terminal elements in the form of metal plugs 2 press-fitted into casing l and fixedly held in position by steel pins 3 projecting transversely through casing 1 into metal plugs 2. Each of terminal plugs 2 defines at the axially inner surface thereof narrow grooves 2a having equidistant lateral walls and extending substantially radially outwardly from the center regions of metal plugs 2. Reference numeral 4 has been applied to indicate a plurality of plates of an electric insulating material substantially rectangular in cross section and having substantially the same thickness as the width of grooves 2a. Plates 4 are arranged parallel to the axis of casing l and have axially outer ends or edges engaging grooves 2a and thus being firmly frictionally held in position. The radially outer edges of the four plates 4 are notched semicircularly. These notches in plate 4 receive a helically wound fusible element 5 of silver and a helically wound restraining wire 6 which may be made of stainless steel. The ends of parts 5 and 6 are conductively connected to metal plugs 2 and thus form parallel current paths. Reference numeral 7 has been applied to indicate a body of quartz sand inside of easing l filling the preponderant portion thereof, i.e. about 75 percent of the volume thereof, and reference numeral 8 has been applied to indicate an arcextinguishing filler consisting of SiO;, A1 0,, and F 0 inside casing l occupying the portion thereof not occupied by the quartz sand filler 7. Fillers 7 and 8 have an interface A where the particles of quartz forming tiller 7 physically engage the particles forming tiller 8. The filler 8 is compacted or ram packed, i.e. packed so densely as to preclude a mixture of fillers 7 and 8.

Each of the pair of plugs 2 has an axially outer end surface 2b. 'A cylindrical projection 21: of reduced diameter extends axially outwardly from the end surface 2b of each metal plug 2. Each plug 2 and each projection 20 is provided with a central bore 2d. The bore 2d in the plug 2 immediately adjacent filler 8 is relatively large. This makes it possible to fill the filler 8 in a very dense state into casing l, i.e. to compress or compact it by means of a ram to such an extent as to safely preclude any future mixing of fillers 7 and 8 in the absence of a partition or barrier therebetween. The projection 20 of plug 2 immediately adjacent filler 8 is internally screw-threaded and permanently closed by an externally screw-threaded plug 9. The internal screw thread of the projection 20 of plug 2 immediately adjacent filler 8 may serve the additional purpose of mounting the fuse structure on an externally screw-threaded connector stud, e.g. an externally screw-threaded connector stud of a capacitor. Metal plug 2 remote from tiller 8 and the coaxialprojection 2c thereof have a central bore of relatively small diameter intended to receive the blown fuse indicator shown in FIG. 4 on a larger scale. The outer surface of cylindrical projection 20 of plug 2 remote from filler 8 is externally screw-threaded. This makes it readily possible by means of a nut riding on the aforementioned extension to screw a bus bar or a cable shoe (not shown) against the axially outer surface 2b of the aforementioned metal plug 2.

As shown in FIG. 4 the central bore 2d in projection 20 houses a closing cap 10 having a fine bore through which one end of helically wound restraining wire 6 is threaded. This end of restraining wire 6 is attached to a pin 11 biased from right to left by a spring 12 arranged inside of a cap 13. When restraining wire 6 melts the left end of pin 11 is allowed to move under the bias of spring 12 from right to left out of projection 2c, thus indicating that the fuse has blown.

It will be apparent from the above that each of the extensions 2c of plugs 2 performs several functions. The right projection 2c (as seen in FIG. 1) forms a filling duct for fillers 7 and 8 and a connector for connecting the fuse into an electric circuit, and the left projection 2d (as seen in FIG. 1) forms a blown fuse indicator housing and a connector for connecting the fuse into an electric circuit. The fuse shown in FIGS. 1 to 4, inclusive, is intended to be assembled by means of a temporary center post and the passages or central bores 2d in plugs 2 and extensions are a means for spacing plugs 2 by a temporary center post while fusible elements 5 and 6 are wound helically around the radially outer edges of insulating plates 4. Reference may be had to U.S. Pat. 2,740,187 to P. C. Jacobs, Jr. et al. Apr. 3, I956, METHODS OF ASSEMBLING FUSES for a more complete disclosure of the use of temporary center posts in assembling electric fuses.

The ribbon fuse link 5 is intended to provide serially related points of reduced cross-sectional area or necks where fusion is initiated on occurrence of major fault currents. Straight fuse links of this description have been shown in US. Pat. No. 3,391,369 to Frederick J. Kozacka, July 2, 1968 for HIGH- VOLTAGE FUSE. Fuse link 5 is preferably provided with'an overlay 5a of tin or another metal having a relatively low fusing point and capable of severing fuse link 5 by a process of metal diffusion upon reaching the fusing point of the overlay metal. Filler 8 reduces heat transfer from fuse link 5 and thus derates the fuse structure. In other words, the cross-sectional area of fuse link 5 must be increased to impart to it the same current-carrying capacity which it would have if filler 8 were a quartz sand filler. This increase in cross-sectional area of fuse link 5 results in a reduced voltage drop, or reduced i -r losses. The overlay 5a of fuse link 5 has a like derating effect and initiates the interruption of the circuit in which the fuse is included on occurrence of relatively small overload currents of excessive duration. The overlay 5a is situated in the portion of fuse link 5 which is submersed in filler 8.

The terminal plug 2 adjacent filler 8 is provided on the axially inner surface thereof with a pair of clamping screws 14 for attaching the ends of fusible elements 5, 6 to the aforementioned terminal plug. This is necessary or desirable in order to receive the considerable force resulting from the helical configuration of parts 5, 6. In a like fashion the axially inner surface of plug 2 remote from arc-quenching filler 8 is provided with a clamping screw 14 for attaching to it one end of fusible element 5, the corresponding end of fusible element or restraining wire 6 being attached to rod 11, as shown in FIG. 4.

The first step in assembling the fuse structure of FIGS. 1 to 4 consists in spacing metal plugs 2 by means of the aforementioned temporary center post (not shown). Thereafter plates 4 are inserted into grooves 2a and helical fusible elements wound upon plates 4. When these windings are completed the ends of fuse link S are held in position by clamping screws 14 and one endof restraining wire 6 is held in position by one of the clamping screws 14. Upon removal of the temporary center post the terminal plugs 2 are spaced, i.e. the proper spacing of terminal plugs 2 is maintained, by means of insulating plates 4. Removal of the temporary center post allows assembly of the blown fuse indicator of FIG. 4. Thereupon the subassembly 2,4,4,4,4,2 including fusible elements 5,6 is inserted into casing or fuse tube 1. The latter is then filled through the large diameter passage 2d with quartz sand up to about 75 percent of its length, the remainder being filled with filler 8 under a relatively high pressure, or ram packed.

As mentioned above the low thermal conductivity arc-extinguishing filler 8 is a mixture of silica or quartz sand Si0 and iron oxide l e- 0 and aluminum oxide A1 0 Its content of silica is in the order of 50 percent by weight and its content of iron oxide and aluminum oxide is in the order of 20 percent by weight. Filler 8 may include about l0 percent magnesium oxide by weight. This filler results in relatively high are voltages which areprobably due to the presence of silica in it. On the other hand tiller 8 has a much lower thermal conductivity than quartz sand which is probably due to the presence of particles of iron oxide and aluminum oxide in it. The constituent particles of filler 8 are considerably smaller than the constituent particles of tiller 7, and under such conditions no separation of the Si0 Fe 0 A1 0 etc. components of filler 8 takes place provided that filler 8 is carefully compacted or ram packed.

I claim as my invention:

1. An electric high-voltage fuse including in combination:

a. a tubular casing of insulating material;

b. a pair of terminal elements closing the ends of said casing;

c. a helically wound fuse link inside said casing conductively interconnecting said pair of terminal elements;

d. a quartz sand arc-extinguishing filler inside said casing filling the preponderant portion thereof and submersing the preponderant portion of said fuse link; and

. a low thermal conductivity arc-extinguishing filler inside said casing occupying the portion thereof immediately adjacent one of said pair of terminal elements, said low thermal conductivity filler and said quartz sand filler having a common interface, said low thermal conductivity filler being packed so densely as to preclude mixture thereof with said quartz sand filler, and said low thermal conductivity filler including silica in the order of 50 percent and iron and aluminum oxide in the order of 20 percent.

2. An electric high-voltage fuse as specified in claim 1 wherein said pair of terminal elements is formed by a pair of plugs press fitted into said casing, each of said pair of plugs having on the axially outer end surface thereof a coaxial cylindrical projection, one of said pair of plugs immediately adjacent said low thermal conductivity arc-extinguishing filler having a central bore of relatively large diameter extending through said cylindrical projection thereof and being internally screw-threaded and closed by an externally screwthreaded plug, and the coaxial projection of the other of said pair of plugs remote from said low thermal conductivity arc extinguishing filter being externally screw-threaded, having a central bore of relatively small diameter and housing in said central bore thereof a springbiased plunger normally restrained by a fusible wire.

3. An electric high-voltage fuse including in combination:

a. a tubular casing of insulating material;

b. a pulverulent arc-quenching filler inside said casing;

c. a pair of terminal plugs closing the ends of said casing,

each of said pair of terminal plugs having narrow groove means with equidistant lateral walls on the axially inner wherein said groove means extend radially in regard to said pair of terminal plugs and wherein said spacer plates are provided with notches at the radially outer edges thereof engaged by said fuse link means.

5. An electric high-voltage fuse including in combination:

a. a tubular casing of insulating material;

b. a pulverulent arc-quenching filler inside said casing;

c. a pair of terminal plugs closing the ends of said casing, each of said pair of plugs defining on the axially inner surface thereof narrow grooves having equidistant lateral walls and extending substantially radially outwardly from the centerregions of said pair of plugs;

d. a plurality of plates of an electric insulating material having substantially the same thickness as the width of said grooves arranged parallel to the axis of said casing and having axially outer edges engaging said grooves; and

. fusible elements means wound around the radially outer edges of and supported by said plurality of plates conductively interconnecting said pair of terminal plugs and submersed in said arc-quenching filler. 

1. An electric high-voltage fuse including in combination: a. a tubular casing of insulating material; b. a pair of terminal elements closing the ends of said casing; c. a helically wound fuse link inside said casing conductively interconnecting said pair of terminal elements; d. a quartz sand arc-extinguishing filler inside said casing filling the preponderant portion thereof and submersing the preponderant portion of said fuse link; and e. a low thermal conductivity arc-extinguishing filler inside said casing occupying the portion thereof immediately adjacent one of said pair of terminal elements, said low thermal conductivity filler and said quartz sand filler having a common interface, said low thermal conductivity filler being packed so densely as to preclude mixture thereof with said quartz sand filler, and said low thermal conductivity filler including silica in the order of 50 percent and iron and aluminum oxide in the order of 20 percent.
 2. An electric high-voltage fuse as specified in claim 1 wherein said pair of terminal elements is formed by a pair of plugs press fitted into said casing, each of said pair of plugs having on the axially outer end surface thereof a coaxial cylindrical projection, one of said pair of plugs immediately adjacent said low thermal conductivity arc-extinguishing filler having a central bore of relatively large diameter extending through said cylindrical projection thereof and being internally screw-threaded and closed by an externally screw-threaded plug, and the coaxial projection of the other of said pair of plugs remote from said low thermal conductivity arc extinguishing filter being externally screw-threaded, having a central bore of relatively small diameter and housing in said central bore thereof a spring-biased plunger normally restrained by a fusible wire.
 3. An electric high-voltage fuse incluDing in combination: a. a tubular casing of insulating material; b. a pulverulent arc-quenching filler inside said casing; c. a pair of terminal plugs closing the ends of said casing, each of said pair of terminal plugs having narrow groove means with equidistant lateral walls on the axially inner surfaces thereof; d. spacer plates of electric insulating material for said pair of terminal plugs, said spacer plates being substantially rectangular in cross section and having axially outer edges fitting into and engaging said groove means and being positioned by said groove means of said pair of terminal plugs; and e. fuse link means wound around and supported by edge portions of said spacer plates conductively interconnecting said pair of terminal plugs and submersed in said arc-quenching filler.
 4. An electric high-voltage fuse as specified in claim 3, wherein said groove means extend radially in regard to said pair of terminal plugs and wherein said spacer plates are provided with notches at the radially outer edges thereof engaged by said fuse link means.
 5. An electric high-voltage fuse including in combination: a. a tubular casing of insulating material; b. a pulverulent arc-quenching filler inside said casing; c. a pair of terminal plugs closing the ends of said casing, each of said pair of plugs defining on the axially inner surface thereof narrow grooves having equidistant lateral walls and extending substantially radially outwardly from the center regions of said pair of plugs; d. a plurality of plates of an electric insulating material having substantially the same thickness as the width of said grooves arranged parallel to the axis of said casing and having axially outer edges engaging said grooves; and e. fusible elements means wound around the radially outer edges of and supported by said plurality of plates conductively interconnecting said pair of terminal plugs and submersed in said arc-quenching filler. 